In the production of hydrocarbons, such as crude oil and bitumen, from a subterranean reservoir, the characteristic of the formation has a substantial affect on the efficiency of production. It is expected that in the course of most production operations, the flowing hydrocarbon will carry with it an amount of the substrate from which it is being lifted.
In the instance of a formation comprised largely of unconsolidated sand particles, the flowing hydrocarbon will tend to carry excessive sand with it. The sand thus entering the well casing or liner forms a part of the flow and will eventually have a detrimental effect on the overall operation, as well as on the equipment.
For example, the size of the sand particles could be such that there is a propensity to block or at least partially plug holes and passages through which the flow passes. Further, the abrasive nature of the sand results in the wearing away, or damage to parts which make up the well completion.
Since the combined sand and hydrocarbon flow will have to be treated and separated after being produced, the equipment needed for such separation generally constitutes a major part of the production facility in which sand is a prevalent factor.
It can be appreciated that in the instance of bitumen production from tar sand environment, and the production of viscous crude oil, the problem of sand control can pose a major consideration. In the specific instance of bitumen, the normal thermal stimulation of a substrate through the use of hot fluids such as steam, will tend to promote the flow of sand. As the bitumen or viscous crude is released, the resulting mixture or emulsion will carry along with it, in its flow to the production string, varying sized sand particles.
It has been determined that where the hydrocarbon holding formation constitutes a relatively thin subterranean layer, there are advantages in using horizontal wells. The latter, for example, extend concurrently with the productive layer and can be more economical than a series of vertical wells, all of which pass through the layer at spaced apart points. In the instance of a horizontal well, by stimulating the formation adjacent to the well, the viscous hydrocarbon can be caused to flow and gravitate toward the single well. There it will be produced as a hot mixture or emulsion.
Further, in the instance of horizontal wells which are utilized in tar sands, the problem of excessive sand production in particularly acute. As above noted, the hot bitumen is stimulated and caused to assume a fluid state, thereby carrying with it substantial quantities of sand. The latter will then enter the wall perforations in the horizontally positioned perforated liner. These sand particles will tend to narrow such passages to a minimum opening, or completely obviate flow therethrough.
Efforts have been made through the use of replaceable screens, to minimize this flow of sand into a horizontal producing well. However, the very nature of the well, because it extends horizontally rather than vertically, introduces problems not heretofore contemplated with respect to the in-situ formation of a suitable gravel pack.
Gravel packing is considered the most flexible and prevalent way of minimizing sand production in vertical wells. Such packs are further considered to be of comparable efficiency if they can be adapted to be utilized in conjunction with a horizontal well.
The state of the art relative to in-situ gravel packing of hydrocarbon producing wells covers a broad spectrum of apparatus and methods. Essentially, however, the art is concerned primarily with packing of vertical and/or deviated wells, with open or closed casing. In such wells, gravel injection can be achieved primarily by a gravity flow.
Examples of this type of gravel pack are disclosed in U.S. Pat. No. 4,066,127 and U.S. Pat. No. 4,124,074. In the shown patents, the gravel is introduced through the well and carried into a preformed vertical well cavity whereby to constitute the required sand barrier. This introduction of the gravel is achieved either by feeding the gravel alone, or in the form of a slurry.
In U.S. Pat. No. 2,434,239, the patentee extends the gravel pack concept into a portion of a deviated or sloping well, and even into a portion of a horizontal well. However, the gravel as shown particularly in the patentee's FIG. 3, is introduced to fill the entire borehole. This is achieved by progressively withdrawing the gravel carrying conduit as the borehole fills. The patentee's disclosure lacks the means for providing a gravel pack which surrounds the well liner and forms the necessary peripheral barrier to sand flow.
U.S. Pat. No. 3,261,401 is concerned at least in part with a gravel pack within a horizontal well. The pack in this instance, and as shown in FIGS. 4 and 5, is an integral part of the well liner, and is not installed in-situ.
Toward overcoming the foregoing problems, and for providing an in-situ gravel pack, the disclosed well completion is one that is commenced by first forming an elongated bore. The latter extends substantially horizontally whereby to lie longitudinally through a productive layer or formation.
A perforated well liner or casing, having a diameter substantially less than the diameter of the wellbore, is supportably positioned in the bore in a manner to define an annular passage. Said passage between the casing wall and the adjacent wall of the bore, is furnished with a supporting gravel pack. At least part of the pack supports the liner and is comprised of a gravel size and grade which has been predetermined for the particular formation composition, to best form a barrier to migrating sand particles which would otherwise enter the liner.
The gravel pack is formed in two distinct steps. After the wellbore has been drilled with a horizontal segment, the latter is provided with a foundation bed of unconsolidated gravel. With this support or foundation means in place, the liner is slid along the wellbore for the length of the latter and to its operating position.
Thereafter, the second phase of the gravel pack is achieved by introducing a gravel slurry which is deposited onto the foundation bed, and around the liner.
It is therefore an object of the invention to provide a gravel pack, and method for use thereof in a substrate or formation comprising a sandy composition into which at least one horizontal producing well has been formed.
A further object is to provide a method for forming a gravel pack in situ about a horizontally extending well.
A still further object is to provide a gravel pack and method for applying the same about a well liner that is positioned in a horizontally extending wellbore so that the liner is supported by a gravel foundation.